Composites of highly filled polymeric compositions are becoming increasingly used as materials of construction, particularly for kitchen sinks, kitchen surfaces and sanitaryware, because of their attractive appearance and hard wearing properties. Fluid, curable compositions containing high volumes of finely divided fillers suitable for forming such articles have been described in British Patent No. 1 493 393. This specification describes fluid, curable compositions wherein high volumes of filler of specified particle size are dispersed in a curable material using polymeric diapersants. The use of polymeric diapersants enable compositions to be obtained containing high volumes of finely divided fillers, for example 50% by volume, which have a remarkably low viscosity enabling the compositions to be readily handled for example by pumping. This low viscosity, in turn, enables the compositions to be sold as fluid dispersions which can be readily transported to fabricators who can mould articles in inexpensive low pressure moulds. Although some sedimentation will inevitably occur on storage, the polymeric diapersant maintains the filler particles in a state of stable, deflocculation so that the segment can be readily redispersed by mild agitation to give a dispersion in which the filler particles are substantially uniformly dispersed and will remain so whilst the composition is converted from a fluid dispersion to a fully cured composite. The presence of the polymeric diapersant, and its function of keeping the particles in a state of stable deflocculation, not only enables a low viscosity, redispersible dispersion to be obtained, but ensures that compatibility of the components is maintained as the composition is cured so that a cured product free from cracks and flaws is obtained.
It is also possible to fabricate moulded articles which have a viscosity too high to be of practical value as transportable, low viscosity, redispersible compositions. Nevertheless, these compositions are useful where the fabrication operation is carried out at the same location as the composition is prepared and where storage and redispersion are not a problem. These compositions must also contain fillers which are properly dispersed within the curable composition to avoid problems of flocculation and cracking on polymerisation.
Although these compositions are widely used in the applications described above a small proportion of moulded articles fail prematurely in service, when subjected to thermal cycling such as experienced by a kitchen sink subjected successively to very hot and cold water. Curable compositions have now been devised which provide moulded articles having an improved thermal resilience, i.e. an improved performance in respect of the damage tolerance thermal shock test and often in respect of the thermal shock test, both of which are hereinafter described.